Double wrapped prestressed concrete pipe



Oct. 8, 1957 k. E. JAMES ,808,85

I DOUBLE WRAPPED PRESTRESSED CONCRETE PIPE Filed Oct. 26, 1953 KEN/v5 7w 5. J4M5 INVENTOR.

DOUBLE WRAPPED PRESTRESSED CONCRETE PIPE Kenneth E. James, Baldwin Park, Calif., assignor to United Concrete Pipe Corporation, Baldwin Park, Califi, a corporation of California Application October 26, 1953, Serial No. 388,233

3 Claims. (Cl. 138-66) This invention relates to improvements in reinforced concrete pipe.

Heretofore reinforced concrete pipes have been manufactored by spinning a steel cylindrical shell about its aixs and positioning therein a moldable self-hardening cementitious material. This cementitious material on spinning with the shell distributes itself over its interior, compacts itself and expells excess water. The cementitious material is then allowed to be or caused to be cured and hardened. Thereafter, relatively heavy steel wire is helically wound under tension about the shell and its ends are anchored thereto, and following this the shell and wrapped wire thereabouts have been coated with a selfhardening cementitious material. In this manner, the tension of the wire wrapping causes desirable compressive stresses to be developed in the shell and in the cementitious lining therein. 7

An object of the present invention is to provide a new reinforced concrete pipe of this general character but which is meritorious in that it has tensile stressed reinforcing steel advantageously disposed. In accordance with the present invention the steel shell is similarily spun and the cementitious lining is formed therein after which the steel shell is wrapped or wound with heavy wire under tension, developing compressive stresses in the shelland lining. The shell and wrapping are thereafter coated with a self-hardening cementitious coating which is allowed to cure and harden and thereafter the coating is again wrapped with heavy wire under tension. This second wrapping of wire is also coated or covered with an external coating of self-hardening cementitious material. In this manner the first coating of cementitious material that is applied to the exterior of the shell and the first wrapping has compressive stresses developed therein by the second wrapping. These compressive stresses are, in turn, transmitted through the first wrapping and the shell to the lining. The result is a reinforced concrete pipe wherein the lining and shell may be regarded as sub jected to the greatest compressive stress. The first coating is also under compressive stress but it is normally not as great as the total compressive stress'developed in the shell and lining. The external coating i sgenerally without any stress present therein and is relied, upon primarily as merely the protector for the second wire wrap ping. In this manner there is no sharp line of demarcation between the heavily stressed material and unstressed material. Or, if such a line exists, his not so highly pronounced.

The bond between the cementitious material and the steel inner wrapping and the steel shell can consequently be superior due to the state of compression of the surrounding first cementitious coating. Furthermore, the reinforcing afforded by the spaced tensile stressed lwire wrappingsbecomes advantageously arranged with relation to the cementitious material to give the desired reinforcing effects thereto under the loads to which pipe of this character is normally subiected.

nited States Patent O Patented Oct. 8, 1957 With the foregoing and other objects in view, which will be made manifest in the following detailed description and specifically pointed out in the appended claims, reference is had to the accompanying drawings for an I illustrative embodiment of the invention, wherein:

The figure is a sectional view illustrating the adjacent ends of two pipe sections manufactured in accordance with the present invention and illustrating one form of joint that may be used to connect these pipe sections.

Referring to the accompanying drawings wherein similar reference characters designate similar parts throughout, each pipe section consists of an impervious steel cylindrical shell 10 which extends the major portion of the length of the concrete pipe section. Adjacent one end thereof there may be welded or otherwise secured a steel bell ring 11 and adjacent the other end there may be welded or otherwise secured a steel spigot ring 12. These rings are capable of telescoping one within the other and may be sealed, such as by a rubber gasket 13. Other types of joints may be used between the adjacent ends of adjacent pipe sections and the particular joint shown is of no great import insofar as the present invention is concerned.

In the manufacture of the improved pipe the shell 10 together with its rings 11 and 12 is spun about its axis at a high speed of rotation. A quantity of self-hardening cementitious material 14 is positioned therein while the shell is spinning and by the centrifugal forces developed therein it will distribute itself over the interior of the shell forming a lining of adequate thickness. This cementitious material may be a Portland cement concrete composed of about one part cement to approximately three parts of aggregate. There may be added thereto aluminum powder which is used as an expanding agent for the concrete and other expanding agents may be used in lieu thereof, if desired. Such expanding agents are designed to cause the lining 14 to expand as it cures and sets. Either water curing or steam curing may be used to cure the lining and to cause it to harden.

When such a curing has been effected a heavy wire wrapping 15 is wound. about the shell 10 under tension. This wrapping is helically wound against the shell so that it has .spaced convolutions. The ends of the wire wrapping 15 may be anchored to the shell or to its rings 11 and 12, such as by being welded thereto. The tension of the wirewrapping 15 develops compressive stresses within the shell 10 which are transmitted therethrough to the lining 14. When the wrapping 15 has been positioned the shell and wrapping are coated with a selfhardening cementitious material 16, such as Portland cement concrete. This may be thrown against the exterior of the shell and the surrounding wrapping, such as byan apparatus disclosed in my prior Patent Application Serial No. 18,555, filed April 2, 1948 (now Patent 2,651,404).

The coating 16 after it has cured and hardened is wrapped with a heavy wire wrapping 17 which s also wrapped under tension. The convolutions of this wrapping are helical and end convolutions may be positioned the exterior of the pipe. This coatingmay also'be in the form of a Portland cement concrete and can either be thrown against the coating 16 and the surrounding Wrapping 17 or it may be poured about the coating and the wrapping. For some purposes a poured external coating may be regarded as superior to a coating that is applied by projecting the constituents against the coating 16 at sive stress but the compressive stress therein is only that developed by the outer wrapping 17. The external coating 18 may be regarded as being unstressed. In this manner from a maximum of compressive stress in the lining 14 there is a gradual change in compressive stress from the lining to the external coating 18 so that there is no sharp line of demarcation betweena heavily stressed layer and a non-stressed layer.

In the normal use of pipe of this character the pipe is subjected to high internal pressures tending to burst the pipe. These pressures are resisted by the high compressive stresses in the lining and should any small cracks develop in the lining the high compressive stress existing therein is conducive to autogenous healing of the concrete. Usually these pipes are buried so that they are subjected to external loads as well as the internal load above mentioned. These external loads may be greatest at the top and bottom of the pipe but they also cause bending stresses at the sides of the pipe. 7

With the two wrappings and 17 spaced from each other these wrappings function not only to develop compressive stresses in the concrete deposited within them but they also function as steel reinforcements for the concrete. Under the various loading conditions it will be appreciated that either the wrapping 15 or'the wrapping 17 and sometimes both will be most advantageously positioned within the wall thickness of the pipe'to function as eificient reinforcements. Thus if the pipe is regarded as being heavily loaded externally on the vertical diameter tending to flatten the top and bottom of the pipe and tending to cause cracks'to open in the lining 14 at the top and bottom of the pipe, the shell .10 and the inner wrapping 15 are advantageously located to carry tensile stresses which would resist such opening due to the .fact'that they are located near the interior surface of the pipe under the same loading conditions. Portions of the pipe located at the ends of a horizontal diameterwould be under stress tending to open cracks in the coating 18 on the. exterior of the pipe; The outer wrapping 17 is advantageously positioned near the exterior surface of the pipe to carry tensile stresses which would resist such external cracking. Consequently, the spacing of the two wrappings 15 and 17 causes these wrappings to be advantageously located and to be most beneficially used under external loading conditions not only at the top and bottom of the pipe but also at the sides and at intermediate points. The concrete is also under a stressed condition which is advantageous.

As illustrated on the drawing the spacing between the convolutions of the outer wrapping 17 is somewhat greater than the spacing between the convolutions of the inner wrapping 15. This is not necessarily true under all conditions. However, if the space of the outer wrapping should be the same as that of the spacing of the inner wrapping 15 the convolutions preferably bear staggered relationship to each other so that the effect of the outer wrapping in developing stresses in the coating 16 is somewhat distributed with respect to the stressing developed by the inner wrapping on theshell and lining.

The tension under which the outer wrapping 17 is wrapped about the pipe may be either the same as or less than the tension under which the inner wrapping 15 is applied. It seldom, if ever, will exceed the tension shell.

In assembling adjacent pipe sections the spigot ring is telescopecl into the bell ring together with gasket 13 and the spaces between the ends are filled with cementitious material, indicated at 19 and 20.

From the above-described method and resulting prodnot, it. will. be appreciated that an improved reinforced concrete pipe has been developed which is highly advantageous with respect to the distribution of desirable stresses in the concreteand in the distribution ofthe a steel reinforcemenfthroughout the wall thickness of the pipe. This constructionis also quite advantageous considering such factors as plastic flow of the concrete under stress and creep of the steel of the shell and of the wrappings. It will be appreciated that the pipe may be manu factured in accordance with conventional and accepted methods of manufacture but by the addition of the second wrapping 17 about thte coating 16 and the additionof the external coating 18 the wrappings are not only adequately protected but proper arrangement and distribution-of high tensile reinforcementcan be secured.

Various changes may be made in the details of construction without departing from the spirit and-scope of the invention as defined by the appended claims. a

I claim:

1.. A concrete pipe comprising a cylindrical. steel shell having a self hardening-cementitious lining on the. interior therof, a tensile stressed .helically wound heavy wire wrapping about the shell, a selt-hardening cementitious coating about the shell and wrapping, a second tensile stressed helically wound heavy wire wrapped about said coating, and an exterior self-hardening .cementitiouscoating about the first-mentioned coating and said second tensile stressed wrapping whereby the first mentioned coatingis under compressive stress exerted by the second tensile stressed wrapping-and the shell and lining: are together under compressive stress exerted by both wrappings.

g 2. A concrete pipe comprising a cylindrical steel shell having a self hardeningcementitious lining on the interior thereof, a tensile stressed .helically wound heavy wire wrapping about the shell, a self-hardening. cementitious coating about the shell and wrapping, a second tensile stressed helically wound heavy wire wrapping about said coating, and an exterior self-hardening cementitious coating about the first-mentioned coating and saidsecond tensile stressed wrapping, the tensile stress of the second wrapping beingv no greater than that of the first i 3. A concrete pipe comprising a cylindrical steel-shell having a self hardening cementitious lining onftheinterior thereof,v a tensile stressed helically wound heavy wire wrapping about the shelLa self hardening cementitious coating about the shelland wrapping, a second tensile stressedhelica'ily wound heavy wire wrapping about said coating, and an exterior self. hardening cementitious coat.- ing about the first mentioned coating and said second tensile stressed wrapping, the convolutions of said wrappings" bearing a staggered relationship with respect to each other.

References Cited in the file of this patent .STATES PATENTS 

